The solid-state NMR of quadrupolar nuclei is becoming more important to date. The anisotropy of quadrupolar coupling cannot be eliminated by magic-angle spinning. Although large quadrupolar couplings often prevent us from observing NMR signals of quadrupolar nuclei as sufficiently separated signals, the recent development of the equipment and methods including DNP, are spreading out opportunities for NMR observation to a wider range of materials and in deeper levels of information. The quadrupolar parameters, which can be taken from NMR spectra of quadrupolar nuclei, have a potential usefulness to distinguish atoms depending on their local electrostatic environment. MQMAS or STMAS enables us not only to observe quadrupolar nuclei in separated signals but also to get quadrupolar parameters and isotopic chemical shifts of each separated signal component in a 2D spectrum. J- or D-HMQC, CP-HETCOR and related techniques provide us with information about inter-atomic chemical bonding or geometrical correlations. When the sensitivity is insufficient, besides isotope enrichment, for quadrupolar nuclei specifically, enhancement through intra-spin population transfer methods, RAPT, FAM, DFS, WURST, and HS can be applied. WURST, when combined with the QCPMG method, can provide us a method for obtaining NMR spectra for those nuclei having huge quadrupolar couplings, which make it difficult for us to observe the eintire signal shape. This article deals with the NMR methods being standard at present, or becoming standard in the near future, especially for practical samples, for example, mixed samples or amorphous samples. A number of experimental hints and a couple of experimental examples of 27Al and 17O are described.

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Quadrupole Nuclei in Inorganic Materials

  • Toshikazu Takahashi

摘要

The solid-state NMR of quadrupolar nuclei is becoming more important to date. The anisotropy of quadrupolar coupling cannot be eliminated by magic-angle spinning. Although large quadrupolar couplings often prevent us from observing NMR signals of quadrupolar nuclei as sufficiently separated signals, the recent development of the equipment and methods including DNP, are spreading out opportunities for NMR observation to a wider range of materials and in deeper levels of information. The quadrupolar parameters, which can be taken from NMR spectra of quadrupolar nuclei, have a potential usefulness to distinguish atoms depending on their local electrostatic environment. MQMAS or STMAS enables us not only to observe quadrupolar nuclei in separated signals but also to get quadrupolar parameters and isotopic chemical shifts of each separated signal component in a 2D spectrum. J- or D-HMQC, CP-HETCOR and related techniques provide us with information about inter-atomic chemical bonding or geometrical correlations. When the sensitivity is insufficient, besides isotope enrichment, for quadrupolar nuclei specifically, enhancement through intra-spin population transfer methods, RAPT, FAM, DFS, WURST, and HS can be applied. WURST, when combined with the QCPMG method, can provide us a method for obtaining NMR spectra for those nuclei having huge quadrupolar couplings, which make it difficult for us to observe the eintire signal shape. This article deals with the NMR methods being standard at present, or becoming standard in the near future, especially for practical samples, for example, mixed samples or amorphous samples. A number of experimental hints and a couple of experimental examples of 27Al and 17O are described.